Well-established power distribution systems exist throughout most of the United States, and other countries, which provide power to customers via power lines. With some modification, the infrastructure of the existing power distribution systems can be used to provide data communication in addition to power delivery, thereby forming a power distribution communication system. In other words, existing power lines, that already have been run to many homes and offices, can be used to carry data signals to and from the homes and offices. These data signals are communicated on and off the power lines at various points in the power distribution communication system, such as, for example, near homes, offices, Internet service providers, and the like.
While the concept may sound simple, there are many challenges to overcome in order to use power lines for data communication. Power distribution systems include numerous sections, which transmit power at different voltages. The transition from one section to another typically is accomplished with a transformer. The sections of the power line distribution system that are connected to the customers typically are low voltage (LV) sections having a voltage between 100 volts and 240 volts, depending on the system. In the United States, the low voltage section typically is about 120 volts (120V). The sections of the power distribution system that provide the power to the low voltage sections are referred to as the medium voltage (MV) sections. The voltage of the MV section is in the range of 1,000 Volts to 100,000 volts. The transition from the MV section to the LV section of the power distribution system typically is accomplished with a distribution transformer, which converts the higher voltage of the MV section to the lower voltage of the LV section.
Power system transformers are one obstacle to using power distribution lines for data communication. Transformers act as a low-pass filter, passing the low frequency signals (e.g., the 50 or 60 Hz power signals) and impeding high frequency signals (e.g., frequencies typically used for data communication) from passing through the transformer. As such, power distribution communication systems face the challenge of passing the data signals around the distribution transformers.
To bypass the distribution transformer, the bypassing system needs a method of coupling data to and from the medium voltage power line. As discussed, medium voltage power lines can operate from about 1000 V to about 100 kV, and often have high current flows. Consequently, coupling to a medium voltage power line gives rise to safety concerns for the user installing the coupling device. In addition, the coupling device should be designed to operate to provide safe and reliable communication of data signals with a medium voltage power line—carrying high power—in all outdoor environments such as extreme heat, cold, humidity, rain, high shock, and high vibration. Also, coupling around the transformer raises concern that dangerous MV voltage levels may be provided to the customer premises on the data line.
In addition, a coupling device should be designed so that is does not significantly compromise the signal-to-noise ratio or data transfer rate and facilitates bi-directional communication. Furthermore, the coupling device is preferably designed so that it can be installed without disrupting power to customers. These and other advantages are provided by various embodiments of the present invention.